The present invention relates generally to chemical mechanical planarization systems and more particularly to methods and systems for supplying slurry to a single planarization machine or to a plurality of chemical mechanical planarization machines.
In an exemplary, known chemical mechanical planarization (CMP) process, with reference to FIG. 1, surface of a semiconductor wafer 2 is positioned over a planarization pad 5 and moved relative thereto while slurry is supplied to the planarization pad. The wafer is held against the planarization pad by wafer carrier 4. Motor 6 provides rotational movement of wafer carrier 4. Planarization pad 5 is attached to platen 7, which is rotated by a second motor 9. Dispense line 8 is configured for delivering slurry to planarization pad 5. An acoustic transducer 3 is disposed near the output of dispense line 8 for breaking up particles of the slurry just prior its delivery to the planarization process.
Known, exemplary slurries typically include both chemical and mechanical components that facilitate planarization, etching or passivation of a wafer""s surface. An exemplary slurry comprises an aqueous basic or acidic solution, such as aqueous potassium hydroxide (KOH), containing dispersed particles, such as silica or alumina. It is believed that if a slurry is delivered to the polishing pad during its optimal lifespanxe2x80x94i.e., its time window of optimal planarization effectivenessxe2x80x94particles of the slurry remain suspended. Accordingly, there is an aim to provide a consistent and controlled flow of slurry to the polishing pad within its optimal delivery time window.
Exemplary, prior art, slurry distribution systems are shown in FIGS. 2-4. These systems circulate slurry around a fluid loop that supplies slurry to a plurality of polishing machines. In a full-series configuration 210, with reference to FIG. 2, pump 222 pumps slurry 212 from reservoir 211, into forward line 221. A plurality of polishing machines, 250A-250X, are connected in series with forward line 221. Ideally, pump 222 provides enough slurry to the distribution loop so as to maintain a return flow 225 in return line 223, despite slurry demands of the plurality of polishing machines. A known disadvantage of the full series configuration is that servicing of a single polishing machine often requires that the whole distribution loop be shut-down, thereby impacting all polishing machines along the distribution loop.
In another known configuration, with reference to FIG. 3, polishing machines 350a-350x are connected in parallel between the forward 321 and return 323 lines of the slurry distribution loop. Again, the forward 321 and return 323 lines of the distribution loop circulate slurry as provided by pump 222. Each polishing machine receives slurry from a first line 313 which is tapped into forward line 321. A second line 315 returns unused slurry, i.e., that is not taken in by a polishing machine, back to return line 323 of the distribution loop. This parallel-tap configuration 310 of FIG. 3 offers an advantage over the full-series configuration of FIG. 2. In particular, the parallel-tap configuration allows servicing of a single polishing machine, for example, 350x, without having to terminate operation of the other machines associated with the distribution loop.
Although, not specifically shown in the illustrated drawings of the exemplary distribution loops, known fluid flow mechanisms (such as line diameters and ratio""d tap diameters and tees) can be adjusted to establish desired velocities and pressures along different regions of the distribution loop. For example, for a given line fluid flow, a decrease in line diameter can effect a greater velocity therein. Alternatively, by increasing the diameter of the line, the drop in pressure along its length can be reduced (but at the expense of fluid velocity therein). Typically, the diameter of the parallel tapped lines that couple the polishing machines to the distribution loop are kept smaller than that of the forward and return lines of the distribution loop. By keeping the diameters of the distribution loop""s forward and return lines greater than the diameter of the parallel tapped lines, slurry flow favors the distribution loop. Otherwise, slurry could by-pass outer regions of the distribution loopxe2x80x94i.e., by flowing through a parallel tap associated with a given polishing machinexe2x80x94thereby depriving the more distant polishing machines of slurry solution.
Another known distribution loop comprises a simple series-tap configuration 410, as shown in FIG. 4. A plurality of polishing machines 450A-450X receive slurry from the distribution loop by way of respective drop lines 414. These drop lines 414 tap into the distribution loop at different locations 452 along its length. Pump 222 circulates slurry through the distribution loop.
Ideally, pump 222 provides a flow within the distribution loop for establishing a velocity that both replenishes slurry of the distribution line within a given time interval and assures suspension of the particles of the slurry. In the design of slurry distribution systems, a conflicting aim seeks to provide similar pressures at each drop line tap, e.g., 452A through 452X. However, it is known that the greater a velocity of fluid flow within a given line, the greater the drop in pressure across its length. Accordingly, the desire to provide a rapid velocity of slurry flow within the distribution loopxe2x80x94i.e., so as to frequently replenish slurry and preserve suspension of particles of the slurry within the distribution linexe2x80x94this desire for rapid slurry velocity is set against the opposing goal of minimizing pressure drops along the length of the distribution loop.
Further referencing FIGS. 2-4, it is recognized, pursuant the present disclosure, that each drop line 214,314,414 may comprise a dead-zone region that may experience stagnant, or low velocity, conditions in accordance with the slurry demands of their respective polishing machines. For example, upon completing a planarization step, a polishing machine may terminate slurry demand. If the reduced demand ensues, agglomeration and/or precipitation of particles can result within the dead-zone regions of the drop lines.
Further illustrated in FIG. 4, relative to the planarization machine 450A, is another, exemplary prior art re-circulation loop comprising multiple position valve 420 and re-circulation line 422. Valve 420 is disposed near the output of the dispense line. When slurry flow is discontinued to the planarization process, valve 420 is configured to route slurry into re-circulation line 422 for flowing slurry back to drop line 415. In this configuration, slurry continues circulating through the drop line and re-circulation line when slurry is not being delivered to the planarization process. It is noted, however, that when the multiple position valve 420 is configured to deliver slurry to the planarization process, slurry within the re-circulation line 422 may be stagnant.
Accordingly, there exists a need to preserve suspension of particles for slurry within slurry distribution systems, such as drop-lines, or low-flow delivery lines, as are used for delivery of slurry to chemical-mechanical planarization machines. The present invention recognizes these needs and proposes solutions thereto.
In accordance with an embodiment of the present invention, a fluid delivery line is configured to provide slurry to a polishing machine. Slurry is agitated therein by way of plus-minus slurry displacements. Preferably, the plus-minus displacements are performed on a supply side of a metering pump that is used for dispensing slurry of the delivery line to the polishing machine. More preferably, the agitating is performed when a flow of slurry to the polishing machine has been terminated. In accordance with one aspect of this embodiment, an in-line displacement moves a volume of slurry greater than that of the slurry delivery line.
In accordance with another embodiment of the present invention, a planarization apparatus comprises a dispense tube configured with an end for dispensing fluids to a planarization surface. A pump receives slurry from a drop line and is operationally configurable to pump fluid that is received from the drop line to the dispense tube. A displacement exciter is coupled to the drop line and is operationally configurable to provide plus-minus displacements of slurry within the delivery tube. In accordance with one aspect of this embodiment, the displacement exciter comprises a compressible chamber having an interior in fluid communication with the drop line.
In accordance with a further embodiment of the present invention, a slurry distribution loop comprises a fluid line that circulates slurry. A pump is configured to pump solution from a slurry reservoir to the fluid line. An output of the fluid line returns unused slurry to the slurry reservoir. A distribution tap is coupled to the fluid line for drawing-slurry therefrom. A displaceable chamber is coupled in fluid communication with the fluid line. Preferably, the slurry distribution loop further comprises a mixer, e.g., either a passive or active mixer, coupled in-line with the fluid line.
An additional embodiment of the present invention comprises a planarization apparatus having dispense line configured to supply solution to a polishing surface. A delivery line provides at least part of a fluid communication path between a slurry source and the dispense line. A fluid flow control device is configured to control a fluid flow of the fluid communication path associated with said delivery line. A variable volume chamber is coupled in fluid communication with the delivery line. In accordance with an optional aspect of this embodiment, the variable volume chamber comprises a flexible wall and a reciprocating actuator is operatively configurable to reciprocate the flexible wall. Alternatively, the slurry source comprises a variable pressure feed for altering the pressure of slurry presented to the delivery line and the variable volume chamber comprises a passive flexible or movable wall that moves or flexes responsive to pressure changes presented to the delivery line.
In accordance with another embodiment of the present invention, a slurry transport assembly for a polishing machine includes an output line configured to flow solution to the polishing machine and a slurry input line configured for receiving slurry. A multiport valve is coupled between the output line and a slurry input line. The multiport valve has an input chamber and an output chamber coupled together via a fluid communication path that can be selectively closed by a sealing member. The input chamber of the multiport valve is coupled to the slurry input line, and the output chamber is coupled to the output line which feeds the. polishing machine. In a particular embodiment, the input chamber of the multiport valve is defined, at least in part, by a movable or flexible wall. In an alternative embodiment, the input chamber comprises a fixed volume and is coupled to a remote variable volume chamber. Preferably, a rinse line is also coupled to the output chamber of the multiport valve for enabling a flow of rinse solution through the output chamber when the fluid communication path between the input and output chambers is closed by the sealing member.
Another embodiment of the present invention comprises a slurry delivery system having a conduit configured to flow slurry. A drop line taps into the conduit for obtaining slurry therefrom. Additionally, a compressible chamber is operatively coupled in fluid communication with the conduit. Preferably, the system further comprises a sensor that generates a signal in accordance with a condition of the flow of slurry within the conduit. A controller controls operation of the compressible chamber in response to the sensor""s signal.
In yet another embodiment of the present invention, a slurry distribution system comprises a pump disposed between a slurry reservoir and a forward delivery line. The pump is operatively configurable to pump slurry from the reservoir to the forward line. A plurality of drop lines tap into the forward line along a length thereof. A return line returns slurry of the forward line to the slurry reservoir. A variable volume cavity is disposed in fluid communication with at least the return line, and is operable with a displaceable volume for displacing at least a partial volume of the return line. Preferably, the system further comprises one of a passive or active mixer that is coupled in-line with the return line between the slurry reservoir and the variable volume cavity.
A further embodiment of the present invention comprises a chemical mechanical polishing tool set. The tool set includes a plurality of chemical mechanical polishing machines. Conduits couple respective machines of the plurality to a slurry distribution loop for receiving. slurry therefrom. A solution modulator is coupled to the distribution loop and is operable to modulate a flow of slurry of the distribution loop.
These and other features of the present invention will become more fully apparent in the following description and independent claims, or may be learned by practice of the invention as set forth hereinafter.